There are available to musicians, musical instructors and the like a number of known different systems and methods for listening to and analyzing the quality of sound waves being produced by musical instruments or the voice. Some of these known prior art systems are typified by the disclosures in U.S. Pat. No. 4,028,985, issued June 14, 1977 for a "Pitch Determination and Display System;" U.S. Pat. No. 4,122,751, issued Oct. 31, 1978 for an "Automatic Instrument Tuner;" U.S. Pat. No. 4,019,419, issued Apr. 26, 1977 for a "Tuning Device;" U.S. Pat. No. 3,896,697, issued July 29, 1975 for a "Device For Testing the Tune of Musical Instruments;" and U.S. Pat. No. 3,722,353, issued Mar. 27, 1973 for an "Electronic Tuning Device for Visual Tuning of Stringed Instruments." These are not all of the known instruments and methods for analyzing sound signals as described briefly above, but they do typify the type of equipment presently available for sound analysis and teaching or tuning purposes. The difficulty with these known equipments is that they are not easy to operate and simultaneously calibrate while playing an instrument and provide read out displays that are not easily interpreted by an operator, particularly a beginning music pupil.
A primary goal of the present invention is to provide a musical instrument sound signal automatic detection and display system which identifies automatically a note being played without requiring assistance from the instrumentalist playing the musical instrument. While the prior art describes a number of automatic tuners which allegedly are capable of such automatic operation, to the best of the inventors' knowledge such prior art systems are commercially impractical and no devices are currently being marketed which have an automatic identification feature comparable to that made available by the present invention. The current, commercially available, tuners all require that the musician or other operator specify in advance the note he wishes to tune to, generally by setting a twelve position switch to the desired note in advance of playing the note. Thus, it is not possible to tune several different notes without requiring that the operator remove his hands from the instrument he is playing to change the note selector on the tuner. The system made available by this invention does not require that the instrument operator specify the note to be played in advance since a note being played will be determined automatically by the novel detection and display system. This allows the musician or other operator to play any note on his instrument or play different notes, in any order, either in scales or at random to the best of his ability without requiring that he break his concentration to manipulate the sound signal automatic detection and display system.
The lack of foreknowledge of a note being played, is responsible for the difficulty encountered in designing a suitable sound signal processor or "front end sound detector" which can separate the fundamental frequency of a note being played from the harmonics normally present in a musical tone. In some instruments, such as the oboe, the harmonics are many times stronger than the fundamental. Additional complications are introduced by the presence of background noise and by the wide variation in the amplitude of different sound signals to be analyzed.
The conventional approach utilized in currently available tuners is to extract the fundamental frequency of a sound wave being analyzed by using a narrow tuned filter or phase locked loop, which is set in advance by the musician for a particular note to be played. Obviously, such known techniques could not be used in the present system due to lack of advance knowledge of which notes will be present in a sound wave being analyzed. Accordingly, the invention makes available a novel front end sound signal detector, which automatically works over a wide range of frequencies. An alternate peak detector is the principal element employed in this novel front end sound detector. It can extract the fundamental frequency of any input sound signal without advance knowledge of the approximate frequency value, since its operation does not depend on tuned circuits. Automatic gain control and automatic filter stages enhance the performance sufficiently to make the resultant output processed signal really useful. The only way that the musician or other operator of the system has to specify in advance information about a note to be played is with a low/normal range switch which extends the useable range of the detector to include some very low notes at the expense of some increased sensitivity to background noise. Even with the selector switch in the "low" position, the full range of notes in the musical scale can be processed by the system.